Method of diffusion bonding a fluid flow apparatus

Abstract

The present invention relates to a method of diffusion bonding of steel and steel alloys, to fabricate a fluid delivery system of the kind which would be useful in semiconductor processing and in other applications which require high purity fluid handling.

1. A method of uniaxially diffusion bonding sheets of stainless steel or stainless steel alloy to form a semiconductor apparatus fluid flow handling structure which is capable of functioning in corrosive environments, said method comprising:
 selecting a plurality of sheets to have a chemical composition and structure which will provide an appropriate balance of mechanical strength, chemical compatibility, corrosion resistance and high leak integrity with respect to the fluids which are to flow in the fluid flow handling structure; 
 pattern etching or pattern machining at least two sheets to produce a depression, or a through hole, or a combination thereof in surfaces of said at least two sheets; 
 processing bonding surfaces of said at least two sheets to have a surface finish roughness which is less than 10 Ra micro-inches; 
 processing bonding surfaces to have a cleanliness such that a total ionic contamination of less than 0.33 micrograms per square inch or less is present on said bonding surfaces; 
 processing said at least two sheets to have a flatness of ±0.001 inches overall and ±0.0005 inches over any 4 square inch area; 
 processing said at least two sheets to exhibit parallelism of ±0.001 inches overall and ±0.0005 inches over any 4 inch square area in an unrestrained condition; 
 processing said bonding surfaces of said sheets to remove oxidation, so that an oxidation thickness on said bonding surface ranges from about 40 Angstroms down to about 10 Angstroms; 
 aligning said plurality of sheets relative to each other in a manner which produces a desired fluid flow handling structure; and 
 subjecting said plurality of sheets to a pressure sufficient to cause a crush ranging between about 0.75% and about 3.0%, as measured when using uni-axial diffusion bonding, while said plurality of sheets are at a temperature ranging from about 900° C. to about 1,000° C., and at a pressure ranging from about 1,000 psi to about 5,000 psi, for a time period ranging from about 2 hours to about 6 hours, to produce a diffusion bond which contains less than 10% void density across an interfacial bonding line between bonding surfaces. 
 
   
   
     2. A method in accordance with  claim 1 , wherein said at least two sheets are processed to have a thickness tolerance of about +0.001 inches, unrestrained. 
   
   
     3. A method in accordance with  claim 2 , wherein said at least two sheets are processed to have a final sheet thickness within 0.003 inches over the desired final thickness. 
   
   
     4. A method in accordance with  claim 1 , wherein said at least two sheets are processed to have a thickness variation within ±0.0005 inches when stop blocks are used during the application of pressure to achieve diffusion bonding. 
   
   
     5. A method in accordance with  claim 1 , wherein said surface finish roughness ranges between 0.5 micro-inches Ra and 10 Ra micro-inches Ra. 
   
   
     6. A method in accordance with  claim 1 , wherein said bonding surfaces of said sheets are processed to remove oxidation, so that an oxidation thickness on said bonding surface ranges from about 40 Angstroms down to about 20 Angstroms. 
   
   
     7. A method in accordance with  claim 1 , wherein subsequent to said diffusion bonding, an interior surface of a fluid flow conduit within said fluid flow handling system is electropolished, or treated with an ultrasonic-energized slurry, or a combination thereof, whereby said interior surface is made smoother. 
   
   
     8. A method in accordance with  claim 1 , wherein a plurality of fluid flow handling structures are created during processing of a single assembly of sheets. 
   
   
     9. A method in accordance with  claim 1 , wherein prior to the alignment and diffusion bonding of said sheets, said sheets are bagged in a sealed bag and stored, awaiting further processing. 
   
   
     10. A method in accordance with  claim 9 , wherein said sealed bag contains an atmosphere which protects said bagged sheets from corrosion. 
   
   
     11. A method in accordance with  claim 1 , wherein subsequent to diffusion bonding of said fluid handling structure, said structure is bagged in a sealed bag which protects said structure during shipment and storage prior to use.